The International Cessna^® 170 Association

Hello all, I have a 1948 170 with an o-300. The motor is currently being overhauled. I'd like to replace the baffling. Does anyone have a recommendation on purchasing a kit?

Thanks!

AirForms probably makes the best ones out there (if not the only ones).
http://www.airforms.biz/index.php?route ... uct_id=667

Lownslow, Thanks

My mechanic was thinking he could adapt the new baffling to eliminate the plenum or inner cowl. Would this be possible?

Thanks

The subject of eliminating the inner pressure plenum comes up from time to time. Here are the points most often brought up.

The early top cowl is not the same in design as the later pressure cowl in that the sides do not open in the later as the early cowls do. The latches that hold the early cowl closed are a bit flakey. They pop open when not under pressure. Imagine them under pressure. Even with a secondary locking method which I think mandetory in any case. Maybe this was the reason Cessna went away from the early cowl design in favor of the newer design.

Other discussions relate to approval for the mod which quite frankly would always be in question as far as I'm concerned.

Has it been done. Yes. Usually in conjunction with an engine upgrade such as a larger Lycoming or Continental and in those cases new design baffle and a pressure cowl is part of the STC.

I wouldn't do it. Besides questions of airworthiness, what will it get you?

Bruce, This is a very good point, the latches are flakey at best, I agree.

Thanks

Aryana wrote:If anyone buys from Airforms, spring for the 50% premium for their hammer powdercoating option...you won't regret it.

Aryana , don't know when you bought yours but it is only another $155 for the hammer powder coating. (About 12% extra).
http://www.airforms.biz/index.php?route ... uct_id=667

I called and talked to Airforms and the gentleman stated that the kits they sell doesn't apply to my S/N 18549 1948 170. Does anyone know what difference there may be?

Thanks!!

Arash, Airforms has the baffles for the '49-52 170 models with the plenum (in addition to the baffles for the later year models without the plenum). Just not for the '48 year model. I don't know why, or how the '48 baffles differ from the others (with or without the plenum).

It is sort of mystifying, as every baffle part number that I have checked has been the same part number for the '48 as for the A model.
(I may not have checked them all.)

The '48 is the same as the '49. Someone needs to clue Airforms into that fact.

I bought a set of Airforms B model baffling (used) for my A model, due to the fact the the original baffling was junk I had modified the firewall heater valve and added the interior B model ducting\plenum as well. I also went to a B model Hanlon wilson muffler setup, and updated the carb heat elbow setup . The B model airforms baffling had to be modified as well by trimming the aft "bulkhead" as well to fit the profile of the A cowling. It was a bit of work, but fits well. I replaced all the stock cowl latch parts that were worn or weak. The cylinder side baffling only needed a bit of modification on one side to fit correctly. All this work was done during a complete, and I do mean complete restoration, which finally was completed after 7 years, and was test flown in August this year. After reviewing the video from the go pro out the windshield, there was no buldging or shaking in the upper cowl during all phases of flight. Having said that, I would concur with Bruce's concern of changing to a pressure cowl, and the issue with the latches. I had considered using the camloc addition setup seen in various threads, and now considering the possibility of latch failure under the new "pressure" , I will and would recommend an additional saftey method to secure the A model latches.
As far as cooling is concerned, during the 1st 1.5 hrs of break in, per continental SB, the chrome cylinders never even got to 400 f (rear aft cylinder)and the oil peaked at 235 and then dropped back . Oil consumption was 1/2 qt during 1.5 ,( some was blown out of breather, started with 7 qts) and second flight of 1.5 hrs was about the same. Using F&M oil filter adapter. Also have Bartone exhaust pipes as well.
What you get is improved cooling (per cessna), no doghouse to rub on and wear the upper cowl, (mine needed repair from just that) less parts and full access to the top of the engine with the side cowls open. I do not however have any reference of temps before the mod , as I bought the aircraft as a project in pieces and restored it. My 2 cents...

Rick

All, Thanks for all the great input! I'm going to likely order the '49 part, powder coated as suggested.

The matter of converting an early style to an "ad hoc" later pressure type can be complicated. If one changes-out the entire outer cowl and uses all the baffles from that type, such as the intercylinder and cylinder-base baffles,...to the point where it is identical to later pressure cowls, then it's probably OK.

But the matter of using airframe/cockpit instruments such as cylinder head temps to determine if an ad hoc system keeps the engine within temperature limits is not very legitimate, IMO. A CHT gauge tells the temp at the cyl head., but it does not tell the barrel temps. And most only sample one cylinder. And it's unlikely to have been calibrated properly for the purpose.

I'm trying to say that changing it out to the point where it "looks good" and the CHT gauge does not complain is hardly a valid method of assuring the engine is being properly cooled without hot-spots.

The matter of converting an early style to an "ad hoc" later pressure type can be complicated. If one changes-out the entire outer cowl and uses all the baffles from that type, such as the intercylinder and cylinder-base baffles,...to the point where it is identical to later pressure cowls, then it's probably OK.

But the matter of using airframe/cockpit instruments such as cylinder head temps to determine if an ad hoc system keeps the engine within temperature limits is not very legitimate, IMO. A CHT gauge tells the temp at the cyl head., but it does not tell the barrel temps. And most only sample one cylinder. And it's unlikely to have been calibrated properly for the purpose.

I'm trying to say that changing it out to the point where it "looks good" and the CHT gauge does not complain is hardly a valid method of assuring the engine is being properly cooled without hot-spots.